National Geographic has a gallery titled GLOWING ANIMALS: Pictures of Beasts Shining for Science, which includes pictures of animals that have been engineered to become fluorescent using Green Fluorescent Protein (GFP) extracted from jellyfish, as well as animals that glow naturally for one reason or another.

In 1961 researcher Osamu Shimomura of the Marine Biological Laboratory in Massachusetts noticed a molecule in this jellyfish that glowed bright green under ultraviolet light (as pictured).

After extracting the molecule from 10,000 specimens, Shimomura found the protein that creates the glow.